Non-irradiative methods to create radioactive isotopes?

Question

My understanding is that the primary methods with which one can create a radioactive isotope are 1) just waiting for the isotope you want (by means of nuclear decay), or 2) some kind of induced radiation, where a stable material is bombarded with nuclear particles to create a radioactive isotope (as occurs in the process of creating medical isotopes by using a cyclotron).

Both of the aforementioned methods require the use of irradiation, or the existence of an already radioactive substance. Are there other ways to generate a radioactive isotope? Can we use electricity to generate high temperature/pressure conditions to make it radioactive?

Answer 1

You can create some (but not all) radioisotopes through “photoproduction,” in which the bombarding particles are photons, or by irradiation with stable particles, such as electrons or ionized nuclei. It is a question of the energies involved.

You used to have, in your home, one or more electron accelerators. They were called “cathode ray tubes” and were most commonly used for televisions and computer monitors, before flat-panel displays were affordable. Those devices contained a large vacuum tube, with a metal filament at the back hot enough that thermal electrons could leak off into the vacuum, where they were accelerated towards the screen with an energy of a few kilo-electron-volts, or keV. The kilovolt electronics were why televisions had lots of “do not disassemble” warnings on them, and the electron steering in the vacuum is why your TV went wonky if you held a magnet nearby.

Kilo-eV electrons make x-rays when they stop, which is why your TV had heavy leaded glass in front of the display phosphor. A very similar electron accelerator with energies above about ten mega-eV has enough energy to knock a proton or a neutron out of its nucleus. The threshold is called the “separation energy” of the proton or neutron, and is tabulated in various references. If you change the number of protons or neutrons in a nucleus, it is now a different isotope or a different element, and the odds are good that it is radioactive.

I would consider “irradiating with an electron beam” to be a special case of “shooting full of electricity.” It’s slightly easier if you stop the electrons and collect the high-energy x-rays, since then you can have your irradiated sample outside of your vacuum chamber.

As another poster writes, you can’t do this transmutation via chemical means because the energies involved are too small. Electron ionization energies (or “electron separation energies,” to emphasize the parallel) are typically a few electron-volts, a tiny fraction of the mega-eV required to separate a nucleon. Thermal energies are milli-eV. Even at the temperatures and pressures in the core of the Sun, most nuclei don’t undergo nucleon-exchange reactions; this is why the hydrogen in the Sun’s core will last for ten billion years.

Answer 2

You are describing the dream of the alchemist: the transmutation of one chemical element into another. Here is why chemical techniques can't accomplish this task.

Electrochemical manipulations of elements involve rearranging the outermost electrons encircling the element's nucleus which is smaller than the electron cloud by a factor of about ~10^5. This means the nucleus has no participation in the chemical processes taking place when we use electrical current to pull electrons out of that cloud or add electrons to it. Those actions do not change the contents of the nucleus.

Answer 3

As others have said, electron binding energies are orders of magnitude smaller than nuclear binding energies — it is no accident that we call the force that holds nuclei together the "strong" force. It would be very surprising if chemical processes could trigger fusion, and alleged observations must be met with utmost scrutiny, in accordance with the Sagan standard/Laplace's principle.

If the question is generally about creating radioactive isotopes without irradiation, then the answers are: Through fusion, and through spontaneous decay. All radioactive isotopes occurring in larger quantities are the result of nucleosynthesis by fusion in stars, or the result of subsequent fission of even larger such nuclei.

Answer 4

Different nuclides are created either by radioactive decay or through a nuclear reaction, and these involve changes at the nuclear (nucleus) level. Chemical processes occur at the atomic (electron) level and do not affect the nucleus. I am unaware of any process that does involve interactions at the nuclear level that can create new nuclides.